The present invention is directed to a shock-absorbing unit for vehicle barriers and, more particularly, to a shock-absorbing unit for cushioning the impact of a vehicle that hits a safety barrier or a guard rail.
Vehicle barriers such as highway guard rails are designed to stop or to return a misdirected vehicle into a direction approximately parallel to the guard rail with a deceleration acceptable to the occupants of the vehicle. Their primary function is to increase the length of time of the entire event of stopping or redirecting the vehicle, to increase the distance through which the impact energy is alleviated, and to reduce correspondingly the forces of deceleration on the passengers of the car.
Highway guard rails are adapted to intercept an impacting vehicle at a low angle of incidence and are placed in generally parallel alignment with the direction of traffic flow along shoulders of a roadway, along median strips of a divided highway and elsewhere wherever movement off the highway would be hazardous to the vehicle and its passengers. Thus, the guard rail should not only be a mechanical guide but should also function as a shock absorber that dissipates the kinetic energy of the vehicle tending to leave the road and causing immobilization along the guard rail without violently rebounding the vehicle onto the traveled lanes. However, a problem has existed in designing highway guard rails in such a manner that they have both the strength to retain the vehicle and the ability to absorb the force of impact. For example, a conventional highway guard rail structure in common usage comprises lengths of a heavy corrugated or profiled sheet metal strip spanning a plurality of inflexible posts, usually of wood or concrete, arranged in spaced apart relationship along the side of a road, the lengths of sheet metal strip overlapping at their ends. Such a guard rail possesses high elasticity so that vehicles colliding with the rail are often rebounded into the path of moving traffic. Guard rail structures of lower resiliency featuring hollow or foam-reinforced sheet metal profiles and flexible posts are known but suffer the disadvantage of high cost.
Vehicle barriers such as safety barriers are designed to receive the impacting vehicle at a high angle of incidence and are located at the gore noses of highway exit ramps, at the ends of parallel bridges or highway rails, or in front of pilings of overhead crossing bridges, massive posts, signs, buildings or other unyielding obstacles with which an out of control vehicle might collide. Conventional safety barriers have been formed from crushable metals and plastics, but they are permanently deformed by an impacting vehicle and must be replaced after each incident as they are incapable of self restoration to usefulness. Safety barriers featuring metal springs as the means of absorbing the impact elastically store too much of the energy and consequently tend to rebound the vehicle after the impact.
The present invention provides a reusable vehicle barrier having sufficient elasticity to absorb the force of impact while, at the same time, it is not so elastic as to rebound the vehicle into the path of moving traffic.